1. Field of the Invention
The present invention relates to an antenna device having a plurality of arrayed planar antenna elements which can be operated selectively, and to an antenna system employing the antenna device.
2. Description of the Related Art
Japanese Patent Laid-Open Publication No. HEI 8-97620 discloses a multibeam planar array antenna which comprises a plurality of patches arrayed on a dielectric substrate, a feeding section and feeders connecting between the feeding section and the individual patches. The patches form antenna elements for radiating beams of different tilt angles set on the basis of the differences between the lengths of their respective feeders. The feeders includes a feed selecting circuit for selectively starting or stopping feeding to the respective antenna elements.
The disclosed multibeam planar array antenna is capable of producing multibeams corresponding to the respective antenna elements by selectively operating the antenna elements. However, it is strongly demanded that there be provided a reduced size antenna device which allows more minute switching of the directions of multibeams.
Each antenna element of the array antenna is used for both transmission and reception. In the antenna, when separation of transmitted and received signals by a circulator is effected insufficiently, part of the received signals may leak into an associated transmission system, thereby deteriorating the reception sensitivity of the antenna. Consequently, it is demanded that there be provided an antenna device which minimizes or prevents such reception sensitivity deterioration.